Canadian Patent 849,081 issued Aug. 11, 1970 to C. T. Elston, discloses the solution polymerization of alpha olefins such as ethylene and butene in the presence of a transition metal catalyst based on titanium and vanadium. These catalysts do not contain any magnesium component or organic alkyl halides (chlorides).
U.S. Pat. Nos. 5,589,555 (Zboril et al. issued Dec. 31, 1996) and 5,519,098 (Brown et al. issued May 21, 1996), both assigned to Novacor Chemicals (International) S.A. (now NOVA Chemicals (International) S.A.), disclose catalysts for the solution polymerization of alpha olefins. The patents disclose a catalyst system comprising:
(i) a mixture of a trialkyl aluminum compound and a dialkyl magnesium compound; PA1 (ii) a reactive chloride which may be an alkyl halide; PA1 (iii) a transition metal compound; and PA1 (iv) the reaction product of a trialkyl aluminum compound and an alcohol in amounts up to about stoichiometric amounts to produce a dialkyl aluminum alkoxide. PA1 (i) a mixture of an alkyl aluminum compound of the (R.sup.1).sub.3 Al.sup.1 and (R.sup.2).sub.2 Mg wherein R.sup.1 is a C.sub.1-10 alkyl radical and R.sup.2 is a C.sub.1-10 alkyl radical in a molar ratio of Mg to Al from 4.0:1 to 8.0:1; PA1 (ii) a halide of the formula R.sup.3 X wherein R.sup.3 is a C.sub.1-8 alkyl radical and x is a halide selected from the group consisting of chlorine and bromine; PA1 (iii) titanium tetrachloride; PA1 (iv) VOCl.sub.3 to provide a molar ratio of Ti:V from 95:5 to 70:30; and PA1 (v) an alkyl aluminum alkoxide compound of the formula (R.sup.4).sub.2 Al.sup.2 OR.sup.5 wherein R.sup.4 and R.sup.5 are independently selected from the group consisting of C.sub.1-10 alkyl radicals to provide: a molar ratio of Mg:(Ti+V) from 4:1 to 8.0:1; a molar ratio of Al.sup.1 to (Ti+V) from 0.9:1 to 1.5:1; a molar ratio of halide to Mg from 1.9:1 to 2.6:1; and a molar ratio of Al.sup.2 to (Ti+V) from 2.0:1 to 4.0:1.
The present invention has removed the step in the process of the above patents of the reaction of a trialkyl aluminum compound with an alcohol.
More importantly the patents teach that when vanadium is present together with titanium in the catalyst, magnesium need not be present. Further in the examples which illustrate a mixed titanium and vanadium catalyst system, magnesium and chloride compounds are not present. On a fair reading the patents teach away from the subject matter of the present patent application which teaches that magnesium must be present in the catalyst.
U.S. Pat. No. 4,097,659 issued Jun. 27, 1978 (now expired), to Creemers et al., assigned to Stamicarbon, N. V., discloses a process for producing polyolefins in which a precursor is prepared by reacting an aluminum alkyl halide of the formula R.sub.m AlX.sub.3-m with an organo magnesium compound of the formula MgR'.sub.2 wherein m is a value less than 3, that is the aluminum compound may have 1, 2 or 3 halogen atoms; and R and R' independently may be a C.sub.1 -hydrocarbyl radical. The Creemers patent does not teach or suggest that the first component could be the reaction product of a trialkyl aluminum compound and a dialkyl magnesium compound. In fact the patent teaches against such a system as illustrated by the comparative example in which the first component is prepared by reacting trimethyl aluminum and dibutyl magnesium. The resulting reaction product is then reacted with a transition metal compound. The molar ratio of magnesium and aluminum to transition metal may be from between 0.1:1 and 10:1. The resulting precursor is then activated with an organo-aluminum activator selected from the group consisting of trialkyl aluminum, an alkyl aluminum halide and an alkyl aluminum hydride. Creemers does not teach nor suggest the activator could be a dialkyl aluminum alkoxide. Creemers acknowledges that the transition metal is preferably a titanium compound but that the titanium compound may be replaced by or used in conjunction with a vanadium compound including VOCl.sub.3. However, there is no teaching or disclosure of the ratio of the titanium compound to vanadium compound. In short the patent teaches away from the subject matter of the present invention.
European patent application 0 280 353 in the name of Coosemans et al., assigned to Stamicarbon B. V., published 31.08.88, teaches a two-component catalyst system for the solution polymerization of olefins. The first component comprises a mixture of one or more magnesium compounds, one or more aluminum compounds and one or more transition metal compounds, optionally in the presence of a halogen-containing compound. The second component is an activator which is an organo aluminum compound of the formula R.sup.1.sub.m Al X.sub.3-m. In the first component the ratio of Al:Mg is greater than 1 (claim 1, and page 2, line 26). In the catalysts of the present invention the ratio of magnesium to the first aluminum component is from 4.0:1 to 8.0:1 (therefore the ratio of aluminum to magnesium is from 0.25:1 to 0.125:1) which is well below that specified in the Coosemans patent. It is clear from Coosemans that the preferred transition metal compounds are titanium based. However, Coosemans does disclose that vanadium compounds may be present although there is no teaching on the ratio of the titanium compound to the other transition metal compounds, or heat treatment of the catalyst. In view of the foregoing, the Coosemans patent teaches away from the subject matter of the present invention.
U.S. Pat. No. 4,314,912 issued Feb. 9, 1982 to Lowery, Jr. et al. assigned to The Dow Chemical Company teaches a catalyst which is a reaction product of a transition metal, an organomagnesium compound, and a non-metallic monohalide. In the catalyst the ratio of Mg:Transition metal is from 5:1 to 2000:1; Mg:X is from 0.1:1 to 1:1 (e.g. 1:10 to 1:1) and the ratio X: transition metal is from about 40:1 to 2000:1. In the catalysts of the present invention the ratio of X to Mg is about 2:1 and the ratio of Mg: transition metal is about 6:1. Accordingly the ratio of X to transition metal is about 12:1 which is well below the amount specified in the Lowery patent.
None of the above prior art teaches that catalysts containing combinations of titanium and vanadium oxytrichloride increase the molecular weight of both co- and homo-polymers of ethylene, particularly when the catalyst is subjected to a tempering treatment in accordance with the present invention.
It is very challanging in the solution polymerization of ethylene, to increase the polymer molecular weight without decreasing the catalyst activity. In many cases, it is possible to design a catalyst system to produce a high and useful polymer molecular weight, but the catalyst activity would not be useful on a commercial scale. This invention discloses a Ti-V Ziegler-Natta catalyst system that substantially increases the molecular weight of homo- and co-polymers of ethylene without significant loss in the catalyst activity at high polymerization temperatures.